GENE RECOMBINATION AND HETEROSIS 



303 



The frequency distributions for weight per locule for the Porter X Pon- 

 (lerosa hybrid and parental populations are given in Table 19.5. This table 

 shows that the F2 and Bi to Ponderosa populations have plants falling into 

 classes of greater value than 1.51 1883, the last class in which Fi or Ponderosa 

 plants occur. There are nine such F2 i)lants and three such Ei to Ponderosa 

 plants. If no recombination of genes to produce plants with weight per locule 

 greater than the Fi plants is possible, these plants with values greater than 

 any individual of the Fi population must be chance deviates. Moreover, the 

 chance deviates must be those plants in the F2 population having the I'^ 



TABLE 19.5 



OBTAINED FREQUENCY DISTRIBUTIONS FOR WEIGHT PER LOCULE 

 OF TOMATO FRUITS FOR PORTER X PONDEROSA HY- 

 BRID AND PARENTAL POPULATIONS* 



* Grown at Woodward, Oklahoma, in 1941; original data taken in grams and transformed to logarithms to 

 obtain the means and standard errors of the logarithms. 



genotype or a very similar genotype. The probability of their being chance 

 deviates possessing the Fi or similar genotypes can be determined. 



The mean of the logarithms of the Fi population is 1.168729, and the 

 standard error of a single determination is 0.123426. Calculations (for meth- 

 od see Powers, Locke, and Garrett, 1950) show that only 0.3 per cent of such 

 a genotypic population would be expected to have a value greater than 

 1.511883. The following tabulation shows the theoretical number of gene 

 pairs differentiating the parents, the theoretical percentage of the j)opula- 

 tion of the F2 or Bi to Ponderosa populations possessing the same genotyi)e 

 as the Fi, the theoretical number of plants of the Fi genotype in a popula- 

 tion of 453 F2 plants and in a population of 434 Bi to Ponderosa plants, and 

 the theoretical number of plants of the Fi genotype in the F2 population 

 and in the Bi to Ponderosa population expected to exceed a value of 1.511883. 



An examination of the data opposite one pair of genes in the tabulation be- 

 low shows that only 0.68 Fo plants would be expected to exceed a value of 



